Upon seeing the risen Jesus, Mary Magdalene came to tell the disciples that she saw Jesus risen from the dead. At that time, many of the disciples hid because they were afraid of the Jews. But then the disciples too also got to see the risen Jesus.
When Jesus re-met the disciples, he told them, "Peace be with you." (20:19) He also showed them the body parts. Upon seeing Jesus, the disciples "were glad when they saw the Lord" (20:20).
The disciples were originally expecting fear because the person they have followed for a few years was killed (not to mention various religious leaders targeting followers of Jesus). But seeing the resurrection of Jesus broke their expectations of Jesus. Since they know that Jesus overcame death, they know that Jesus has the power, and they became glad as a result.